The invention relates to a DC/DC up/down converter, comprising inductive energy storage means, switching means and control means, wherein the control means are arranged for selectively operating the switching means for transferring an amount of electrical energy from the energy storage means to an output of said DC/DC converter.
A DC/DC up/down converter of this type is known from International patent application WO 95/34121 in the name of applicant.
In practice, compared to DC/DC up converters, an up/down converter usually requires two extra switching means for realizing the up/down function. This has three major disadvantages. Firstly, in that more chip area is required for integrated circuit DC/DC converters; secondly, in that the series resistance of the circuit as a whole is increased, and thirdly in that higher switching losses occur, in particular in the case of semiconductors switches.
The invention has for its object to propose a DC/DC up/down converter overcoming these disadvantages.
This object is solved, by the present invention, in a DC/DC up/down converter, the control means of which are configured for operatively controlling the switching means of the DC/DC converter for transferring electrical energy to a first output of the DC/DC converter in a down-conversion mode and for transferring electrical energy from the first output to a second output of the DC/DC converter in an up-conversion mode.
In accordance with the present invention two outputs are realized. A first output operated in a down-conversion mode and a second output operated in an upconversion mode. The second output voltage is provided in a two-step conversion cycle wherein energy from the first output is transferred to the second output.
In a preferred embodiment of the invention the DC/DC up/down converter according to the invention comprises:
first and second input terminals;
first and second output terminals;
third and fourth output terminals;
a coil, having first and second connection ends, wherein the second connection end connects to the first output terminal;
first switching means operatively connected to provide a conduction path from the first connection end of the coil to the second input terminal;
second switching means operatively connected to provide a conduction path from the first connection end of the coil to the third output terminal;
third switching means operatively connected to provide a conduction path from the first input terminal to the first connection end of the coil;
first diode means parallel connected to the first switching means, and providing a conduction path from the fourth output terminal to the first connection end of the coil;
second diode means parallel connected to the second switching means, and providing a conduction path from the first connection end of the coil to the second output terminal, and
control means arranged for operatively switching the first, second and third switching means into their closed or conductive state and open or non-conductive state.
Compared with the prior art, the DC/DC up/down converter according to the present invention can be realized with one switch less, thereby saving chip area in the case of an integrated circuit converter and reducing switching losses and output series resistance due to the non-zero resistance of the conduction path of the switching means, in particular in the case of semiconductor switching means.
In the preferred embodiment of the DC/DC up/down converter according to the invention, the control means are arranged for controlling the switching means in a conversion cycle comprising seven different phases:
a first phase wherein the third switching means are in a conductive state and the first and second switching means are in a non-conductive state;
a second phase wherein the first switching means are in a conductive state and the second and third switching means are in a non-conductive state;
a third phase wherein the first switching means are in a conductive state and the second and third switching means are in a non-conductive state;
a fourth phase wherein the second switching means are in a conductive state and the first and third switching means are in a non-conductive state, and wherein current flow in the coil is in opposite direction compared to the second phase;
fifth phase wherein the first, second and third switches are in a nonconductive state;
a sixth phase wherein the first, second and third switches are in a nonconductive state and current flow in the coil is in opposite direction compared to the fifth phase, and
a seventh phase wherein the first, second and third switches are in a nonconductive state and wherein no current flows through the coil.
Preferably, switching means constructed as MOS (Metallic Oxide Semiconductor) transistor means are used, having their control terminal (gate) connected to the control means for controlling the conductive or non-conductive state of the transistors.
Preferably, the DC/DC up/down converter according to the invention comprises smoothing capacitors connected across the output terminals of the first and second output.
The invention further relates to a power supply comprising a DC/DC up/down converter as disclosed above, and arranged for receiving a DC input voltage Vin at its input, and wherein the control means are arranged for transferring an amount of electrical energy from the input to the energy storage means, such that during use the first output of the DC/DC converter provides a voltage Vout1 and the second output of the DC/DC converter provides a voltage Vout2, wherein Vout1 less than Vin and Vout2 greater than Vout1.
The DC/DC converter according to the invention is of particular advantage if applied in a portable electronic appliance, such as, but not limited to, battery powered appliances.